Effects on the Stem of Winter Barley of Manipulating the Source and Sink during Grain-filling: I. CHANGES IN ACCUMULATION AND LOSS OF MASS FROM INTERNODES

Source and sink activities of field-grown barley plants weremanipulated by shading the whole plant or by de-earing at varioustimes after anthesis. The changes in the masses of the internodes,ears, grains and leaves were followed until the grain matured. Shading reduced the mass of ears and grains and, in addition,shading to 45% of incident radiation from anthesis preventedmature internodes from increasing in mass. Severe shading (to9% of incident radiation) from 11 d after anthesis caused thenormal decrease in mass of internodes to occur earlier thanin unshaded plants. Thus, only assimilate in excess of thatrequired for tructural growth was stored in internodes. Lowerinternodes of plants shaded from anthesis lost more of the massthat had been accumulated prior to anthesis than control plants,giving a greater potential pre-anthesis contribution to grainyield. Internodes from plants that were de-eared accumulated more massthan internodes of control plants in one year but not in another,i.e. the potential for internodes to store assimilate appearsto be exploited in some years but not others. The mass of internodesfrom de-eared plants either decreased after that of controlplants or their mass stayed constant. De-eared plants had anincreased number of tillers compared with control plants; thesetillers could have been an alternative sink for assimilate storedin the internodes of de-eared plants. Mobilization of assimilate from internodes is in response todemand for assimilate from grains being in excess of currentphotosynthesis. Key words: Winter barley, stem reserves, mobilization, shading, de-earing     

Changes of enzyme activities associated with the mobilization of carbohydrate reserves (fructans) from the stem of wheat during kernel filling

Wheat plants were grown at a day/night temperature of 18/13°C under glasshouse conditions. Twenty-two d after anthesis, one set of plants was shaded to 50% of the normal photon fluence rate, another was 'degrained' by selective spikelet removal which left only the grains in the five central spikelets; a further set was left as control. Individual plants were harvested at days 22, 30 or 42 after anthesis. Extracts from the peduncle and the penultimate internode were prepared to determine the activities of sucrose phosphate synthase, sucrose synthase, fructan exohydrolase and acid invertase, and to assess the concentration of hexose sugars, sucrose and fructans. Measurements were also made of ear and individual grain weights, and stem f. wt and d. wt. There was a decline in the amount of fructans with time, more pronounced in 'shaded' (source-limited) than in control plants. By contrast, in 'degrained' (sink-limited) plants, the amount of fructans in the stem initially rose, then decreased, with a concomitant increase in the amount of fructose. The shifts in sugar content of the wheat culm reflected both the sink demand of the ear and source activity. The activity of fructan exohydrolase correlated with the carbohydrate changes. Under limited photosynthate assimilation, the mobilization of fructans from the internodes towards the ear was related to an increase in this enzyme, whereas the other enzymes played a less direct role in the mobilization of fructan reserves from the wheat stem.     

Mobilization of fructan reserves and changes in enzyme activities in wheat stems correlate with water stress during kernel filling

Triticum aestivum (wheat) plants grown at a daynight temperature of 1813 °C from anthesis were held as well watered controls, or subject to either a mild (large pot volume) or a more severe (small pot volume) water stress by withholding water from the time of anthesis. Extracts from the peduncle (enclosed by the flag leaf sheath) and the penultimate internode were prepared to determine the activities of fructan exohydrolase and acid invertase and to assess the level of hexose sugars, sucrose and fructans. Measurements were made of ear and individual grain weights and stem fresh weight and dry weight. Plant water relations at the time of each sampling were determined as the flag leaf water potential and the water content of individual organs. Water stress resulted in a shorter duration of kernel filling, smaller kernels at maturity and an earlier loss of stem weight. There was an increase in stem fructose and a fall in fructan level that preceded the loss of dry matter associated with water stress. Coincident with the early fall in fructan content under water stress there was a rise in both fructan exohydrolase and acid invertase in the internodes of stressed plants. This correlation suggests that the conversion of fructans to fructose might have resulted from enzyme induction associated with water stress, but as this conversion occurs before the major export of reserves from the stem it might be only indirectly related to changes in the demand for reserves.     

Comparison of fructan dynamics in two wheat cultivars with different capacities of accumulation and remobilization under drought stress

Remobilization of stored carbohydrates in the stem of wheat plants is an important contributor to grain filling under drought stress (DS) conditions. A massive screening on Iranian wheat cultivars was performed based on stem dry weight changes under well-watered and DS conditions. Two cultivars, Shole and Crossed Falat Hamun (CFH), with different fructan accumulation and remobilization behavior were selected for further studies. Water-soluble carbohydrates (WSCs) and fructan metabolizing enzymes were studied both in the stem penultimate and in sucrose (Suc) treated, excised leaves. Under drought, CFH produced higher grain yields than Shole (412 vs 220 g m(-2)). Also, grain yield loss under drought was more limited in CFH than in Shole (17 vs 54%). Under drought, CFH accumulated more graminan-type fructo-oligosaccharides than Shole. After anthesis, fructan 6-exohydrolase (6-FEH; EC 3.2.1.154) activities increased more prominently than fructan 1-exohydrolase (EC 3.2.1.153) activities during carbon remobilization. Interestingly, CFH showed higher 6-FEH activities in the penultimate than Shole. The field experiment results suggest that the combined higher remobilization efficiency and high 6-FEH activities in stems of wheat could contribute to grain yield under terminal drought. Similar to the penultimate, fructan metabolism differed strongly in Suc-treated detached leaves of selected cultivars. This suggests that variation in the stem fructan among wheat cultivars grown in the field could be traced by leaf blade induction experiments.     

Starch storage in the stems of wheat plants: localization and temporal changes

Background and Aims

Carbohydrate temporarily accumulates in wheat stems during the early reproductive growth phase, predominantly as water soluble carbohydrate (WSC), and is subsequently remobilized during grain filling. Starch has also been reported as a minor storage carbohydrate component in wheat stems, but the details are lacking.

Methods

The accumulation and localization of starch in wheat stem and leaf sheath tissue over a developmental period from 6 d before anthesis to 35 d after anthesis was investigated.

Key Results

The region of the peduncle enclosed by the flag-leaf sheath, and the penultimate internode were the main tissues identified as containing starch, in which the starch grains localized to the storage parenchyma cells. In contrast, the exposed peduncle lacked starch grains. Starch grains were also found in the flag-leaf and second-leaf sheath. Plants grown in low-nitrogen conditions exhibited increased storage of both starch and WSC compared with plants grown in high-nitrogen supply.

Conclusions

The major accumulation and decrease of starch occurred temporally independently to that for WSC, suggesting a different functional role for starch in wheat stems. Starch reutilization concomitant with peduncle growth, and the early development of the reproductive structures, suggested a role in provision of energy and/or carbon scaffolds for these growth processes.Key words: Carbohydrate partitioning, peduncle, starch, wheat stem, storage parenchyma, Triticum aestivum     

Molecular dissection of variation in carbohydrate metabolism related to water-soluble carbohydrate accumulation in stems of wheat

Water-soluble carbohydrates (WSCs; composed of mainly fructans, sucrose [Suc], glucose [Glc], and fructose) deposited in wheat (Triticum aestivum) stems are important carbon sources for grain filling. Variation in stem WSC concentrations among wheat genotypes is one of the genetic factors influencing grain weight and yield under water-limited environments. Here, we describe the molecular dissection of carbohydrate metabolism in stems, at the WSC accumulation phase, of recombinant inbred Seri/Babax lines of wheat differing in stem WSC concentrations. Affymetrix GeneChip analysis of carbohydrate metabolic enzymes revealed that the mRNA levels of two fructan synthetic enzyme families (Suc:Suc 1-fructosyltransferase and Suc:fructan 6-fructosyltransferase) in the stem were positively correlated with stem WSC and fructan concentrations, whereas the mRNA levels of enzyme families involved in Suc hydrolysis (Suc synthase and soluble acid invertase) were inversely correlated with WSC concentrations. Differential regulation of the mRNA levels of these Suc hydrolytic enzymes in Seri/Babax lines resulted in genotypic differences in these enzyme activities. Down-regulation of Suc synthase and soluble acid invertase in high WSC lines was accompanied by significant decreases in the mRNA levels of enzyme families related to sugar catabolic pathways (fructokinase and mitochondrion pyruvate dehydrogenase complex) and enzyme families involved in diverting UDP-Glc to cell wall synthesis (UDP-Glc 6-dehydrogenase, UDP-glucuronate decarboxylase, and cellulose synthase), resulting in a reduction in cell wall polysaccharide contents (mainly hemicellulose) in the stem of high WSC lines. These data suggest that differential carbon partitioning in the wheat stem is one mechanism that contributes to genotypic variation in WSC accumulation.     

Clonal Plasticity in Response to Partial Neutral Shading in the Stoloniferous Herb Potentilla reptans var. sericophylla

Ramet-pairs of Potentilla reptans L. var.sericophylla Franch from forest gap and forest understory were subjected to unshading, shading and partial shading treatments in a pot experiment. The genet biomass, total length of stolons, number of ramets, specific stolon weight, petiole length and specific petiole weight of the plant species under the shaded condition were smaller than those under the unshaded condition. The stolon internode length did not respond to the various treatments. In the plants from the forest gap, the petiloes of ramet grown in the shaded patch were longer as connected to plant part in the unshaded patch than as connected to plant part under the same shaded condition. Such modification of local response of ramet petiole to shading due to physiological integration was not observed in the plants from the understory. There was no effect of connection to ramets in shaded patches on the local response of the rest ramet characters to the partial unshading.     

Effects of shading and of seasonal differences in weather on the growth, sugar content and sugar yield of sugar-beet crops

In 1967 and 1968 plots of sugar beet in two identically grown crops were shaded for successive four week periods starting on 13 June, 18 July and 22 August, and the growth of the plants compared with that on unshaded plots. At the beginning of each period in 1967 some shaded and unshaded plants received additional nitrogen, and in 1968 plants continuously shaded from June to September were compared with unshaded plants irrigated to equalize their water losses with those of the shaded plants. The weather in 1967 was sunny and dry and that in 1968 dull and wet, but the yields of dry matter, and particularly of sugar, of the unshaded crop in the 2 years were similar because, although net assimilation rate (E) was greater in 1967 than 1968, mean leaf area index (L) in 1968 was almost double that in the 1967 crop. Shading decreased the incoming radiation by 56%; it decreased E proportionally in 1967, increasing L slightly, but it decreased both E (by 44%) and L in 1968. The weights of dry matter and sugar in the roots of the shaded crop were consistently smaller at the end of shading and at final harvest in October in both years, and their weights, but not those of the tops or the whole plant, at final harvest over all shading treatments in both years were proportional to the amount of radiation received by the crop between June and September. Although shading greatly decreased the supply of photosynthate to the roots, it did not change the sugar content percentage of dry matter, except in the early stages of growth when the sugar content was rapidly increasing. Sugar content percentage of fresh weight of the roots was consistently decreased by shading, wholly because water content was increased relative to dry matter. Therefore the sugar yield of shaded plants was less because the dry weights of the roots were less, not because the partition of photosynthate between sugar storage and root growth changed. There appears to be a mechanism within the root operating over a wide range of photosynthate supply that maintains a nearly constant proportion of sucrose to non-sugar, contrary to the hypothesis that sugar stored in the roots is photosynthate in excess of what can be used in growth of the plant. However, in the extreme condition of continuous shading which drastically decreased the dry weights of all parts of the plant, sugar percentage of dry matter in the roots was decreased, but only from 80 to 70%. In 1967 extra nitrogen applied at the start of shading increased L and the dry weight of the tops in all periods, but had no effect on the dry weight of roots. Because 1968 was a wet year the irrigation treatment had no effect on E or L except for a slight increase in L during the first period; it had no effect on plant dry weight. Both irrigation and additional nitrogen decreased the sugar content percentage of fresh weight of the roots only by altering their water content; sugar percentage of dry matter was unaffected. None of these changes persisted until the final harvest in October.     

The role of fructan in flowering of Campanula rapunculoides

Inulin type fructan was detected in all vegetative organs of Campanula rapunculoides L. plants. All flower parts contained fructan at some developmental stage. A steady decrease was found in sepals during development. Petals, however, stored fructan in the bud stage. A rapid breakdown during opening of the flower resulted in high concentrations of glucose and especially fructose that may contribute to the osmotic driving force involved in petal expansion. Before complete shrivelling, the hexoses were apparently exported from flower parts. Fructans were hydrolysed and exported from the stamen and style tissue upon flower opening. Similarly, the major fructan reserves in the ovary were broken down almost simultaneously with those in other flower parts. Hexoses did not reach high levels in the ovary, probably because they were rapidly metabolized and/or incorporated by developing seeds.     

匍匐茎草本绢毛匍匐委陵菜对局部遮荫的克隆可塑性

采自林窗和林内生境的绢毛匍匐委陵菜 (PotentillareptansL .var.sericophyllaFranch)“分株对”(即由一匍匐茎节间相连着的两个分株 ,其一为“目标分株” ,另一为“相连分株”)在一户外实验中经历了全不遮荫、全部遮荫和局部遮荫处理。该植物的基株生物量、匍匐茎总长度、分株数、匍匐茎比节间重、叶柄长、比叶柄重在遮荫条件下较小。匍匐茎节间长度没有对遮荫处理发生反应。在局部遮荫处理 ,遮荫斑块的分株的叶柄长度由于连着未遮荫斑块中分株而变得更长。这种克隆整合对克隆形态可塑性的修饰作用只在林窗生境来源的实验植物中观察到。其他克隆生长和克隆形态特征的可塑性在不同生境来源的实验植物间没有差异。     

小麦灌水时期与灌水量对花后果聚糖积累与转运及水分利用效率的影响

于2004-2005年和2005-2006年冬小麦生长季,在山东泰安和兖州进行田间试验,研究不同灌水时期和灌水量处理对冬小麦开花后倒二节间果聚糖积累与转运和水分利用效率的影响.结果表明：全生育期不灌水促进了灌浆后期倒二节间贮藏果聚糖向籽粒的转运.在拔节期和开花期各灌水60 mm,可提高开花后旗叶的光合速率和同化物输入籽粒量及其对籽粒的贡献率,拔节期、开花期和灌浆期各灌水60 mm或拔节期和开花期各灌水90 mm,灌浆后期旗叶的光合速率显著降低,营养器官花前贮藏同化物转运量及其对籽粒的贡献率升高,花后同化物输入籽粒量及其对籽粒的贡献率降低,灌浆后期倒二节间的聚合度（DP）≥4、DP=3果聚糖滞留量增加,不利于果聚糖向籽粒的转运.两个生长季中,拔节期和开花期各灌水60mm处理的小麦籽粒产量较高,水分利用效率最高.拔节期、开花期和灌浆期各灌水60 mm或拔节期和开花期各灌水90 mm,小麦籽粒产量无显著变化,水分利用效率降低.     

干旱调控下小麦RIL群体灌浆期茎秆可溶性碳水化合物积累与转运的遗传分析

以小麦RIL群体(陇鉴19×Q9086,F₈)120个株系及其亲本为供试材料,研究雨养(DS)和正常灌溉(WW)条件下,小麦灌浆期不同发育阶段主茎不同节位可溶性碳水化合物(WSC)含量、转运率及其对籽粒的贡献率,以及穗粒重的遗传特点及各目标性状间的相关性.结果表明: 在两种水分条件下,小麦RIL群体各目标性状变异广泛,变异系数在2.7%～62.1%(DS)和1.9%～52.1%(WW),多样性指数在0.61～0.90(DS)和0.64～0.89(WW),且存在超亲分离.各目标性状表型受基因型、水分环境、节位和发育时期的显著影响.其中,WSC含量受发育时期的影响较大,WSC转运率具有显著的水分和节位主导效应,而WSC转运对籽粒的贡献率受基因型、节位和水分的共同作用.开花初期和灌浆中期WSC含量、花前WSC转运率对籽粒的贡献率之间普遍表现为显著或极显著正相关,且干旱条件下其相关系数更高.各目标性状的遗传力较低(hB₂在干旱条件下为0.31～0.56,灌溉条件下为0.44～0.67),控制各目标性状的遗传基因对数在6～29对(DS)和3～19对(WW).表明该群体对所考察性状有贡献的等位基因在其后代群体中得到广泛分离,其表达易受水分环境的影响,符合典型数量性状特点.     

Fluxes in central carbohydrate metabolism of source leaves in a fructan-storing C3 grass: rapid turnover and futile cycling of sucrose in continuous light under contrasted nitrogen nutrition status

This work assessed the central carbohydrate metabolism of actively photosynthesizing leaf blades of a C3 grass (Lolium perenne L.). The study used dynamic (13)C labelling of plants growing in continuous light with contrasting supplies of nitrogen ('low N' and 'high N') and mathematical analysis of the tracer data with a four-pool compartmental model to estimate rates of: (i) sucrose synthesis from current assimilation; (ii) sucrose export/use; (iii) sucrose hydrolysis (to glucose and fructose) and resynthesis; and (iv) fructan synthesis and sucrose resynthesis from fructan metabolism. The contents of sucrose, fructan, glucose, and fructose were almost constant in both treatments. Labelling demonstrated that all carbohydrate pools were turned over. This indicated a system in metabolic steady state with equal rates of synthesis and degradation/consumption of the individual pools. Fructan content was enhanced by nitrogen deficiency (55 and 26% of dry mass at low and high N, respectively). Sucrose content was lower in nitrogen-deficient leaves (2.7 versus 6.7%). Glucose and fructose contents were always low (<1.5%). Interconversions between sucrose, glucose, and fructose were rapid (with half-lives of individual pools ranging between 0.3 and 0.8 h). Futile cycling of sucrose through sucrose hydrolysis (67 and 56% of sucrose at low and high N, respectively) and fructan metabolism (19 and 20%, respectively) was substantial but seemed to have no detrimental effect on the relative growth rate and carbon-use efficiency of these plants. The main effect of nitrogen deficiency on carbohydrate metabolism was to increase the half-life of the fructan pool from 27 to 62 h and to effectively double its size.     

Fructan contents and dry matter deposition in different tissues of the wheat grain during development

The role of fructan metabolism in the assimilate relations of the grain of wheat (Triticum aestivum L.) was investigated by determination of the dry matter and fructan content of grain components at short intervals during grain filling. During the initial phase of rapid expansion, most of the assimilates entering the grain were partitioned to the outer pericarp. A large fraction of these assimilates were used for the synthesis of fructan. Dry matter deposition and fructan synthesis in the outer pericarp ceased at about 5d after anthesis. At the same time, the endosperm and the inner pericarp and testa started to accumulate dry matter at a fast rate. This was also associated with significant fructan synthesis in the latter tissues. The outer pericarp lost about 45% of its former maximum dry weight between 9 and 19 d after anthesis. This loss was due almost entirely to the near complete disappearance of water-soluble carbohydrates, most of which was fructan. The inner pericarp and testa accumulated dry matter until about mid-grain filling. The fructan contents of the inner pericarp and testa and the endosperm decreased slowly towards the end of grain filling. Most of the fructans in the inner pericarp and testa and the endosperm had a low molecular weight, whereas higher molecular weight fructans predominated in the outer pericarp. The embryo did not contain fructan. The presence of low molecular weight fructans in the endosperm cavity at mid-grain filling was confirmed. It is suggested that fructan synthesis is closely linked to growth-related water deposition in the different tissues of the wheat grain and serves to sequester the surplus of imported sucrose.     

Effects of nitrogen deficiency on accumulation of fructan and fructan metabolizing enzyme activities in sink and source leaves of barley (Hordeum vulgare)

Seedlings of barley ( Hordeum vulgare L. cv. Agneta) were grown hydroponically under continuous light, constant temperature and relative humidity. During the first two weeks, the relative growth rate (RGR) was kept at 25% by limiting only the supply of nitrogen. The cultures were then transferred to nitrogen-free media and the amounts of fructan, starch, sucrose, glucose and fructose in sink and source leaves were measured at 0, 12, 24, 48, 72, 120 and 156 h. The activities of two key enzymes in fructan metabolism, sucrose:sucrose fructosyltransferase (SST), fructan exohydrolase (FEH), as well as acid invertase were also measured in the two types of leaves.
The fructan and starch levels in both sink and source leaves increased during nitrogen deficiency. The highest increase in starch was 200% of the control while for fmctans a 700% increase was recorded. The activity of SST increased parallel to fructan accumulation in sink leaves. However the FEH activity was constant and not affected by nitrogen deficiency. The invertase activity both in sink and source leaves was reduced by nitrogen deficiency. More fructans as well as sucrose and fructose accumulated in source leaves compared to sink leaves both before and after nitrogen starvation. The results show that fructan is the major carbohydrate reserve accumulating under nitrogen deficiency both in sink and source leaves in barley plants. The induction of fructan accumulation in sink leaves caused by nitrogen deficiency is intimately connected with the regulation of SST     

Shading and the capture of localized soil nutrients: nutrient contents,carbohydrates, and root uptake kinetics of a perennial tussock grass

Summary The ability to exploit spatial and temporal heterogeneity in soil resources can be one factor important to the competitive balance of plants. Competition above-ground may limit selective plant responses to below-ground heterogeneity, since mechanisms such as root proliferation and alterations in uptake kinetics are energy-dependent processes. We studied the effect of shading on the ability of the perennial tussock grassAgropyron desertorum to take up nutrients from enriched soil microsites in two consecutive growing seasons. Roots of unshaded plants selectively increased phosphate uptake capacity in enriched soil microsites (mean increases of up to 73%), but shading eliminated this response. There were no changes in ammonium uptake capacity for roots in control and enriched patches for either shaded or unshaded plants. The 9-day shade treatments significantly reduced total nonstructural carbohydrate (TNC) concentrations for roots in 1990, but had no apparent effect on root carbohydrates in 1991 despite dramatic reductions in shoot TNC and fructan concentrations. Enrichment of the soil patches resulted in significantly greater phosphate concentrations in roots of both shaded and unshaded plants, with less dramatic differences for nitrogen and no changes in potassium concentrations. In many respects the shaded plants did surprisingly well, at least in terms of apparent nutrient acquisition. The effects of aboveground competition on nutrient demand, energy requirements, and belowground processes are discussed for plants exploiting soil resource heterogeneity.     

Seasonal Dynamic of Nonstructural Saccharides in a Rhizomatous Grass Calamagrostis Epigeios

Seasonal dynamic of total nonstructural saccharides (TNS) and individual saccharides (starch, sucrose, glucose, fructose, fructans) was followed in rhizomes and stem bases of Calamagrostis epigeios (L.) Roth at two types of meadows communities in the South Moravia (Czech Republic): cnidion and molinion alliances, which differ in their water regime. The TNS were formed mainly by fructans and starch, while glucose, sucrose and fructose were low. The amount of TNS in rhizomes and stem bases of plants from wet cnidion site was higher than in plants from drier molinion site. The seasonal trends of all saccharides were similar in the both sites. During growing season (June to October) the main storage sugar was fructan (18 – 21 % of dry biomass). At the beginning of September the content of fructan decreased to 10 – 12 % and simultaneously the content of sucrose increased from 1 to 3 %. This may increase frost resistance. The content of TNS in the stem bases was lower than in the rhizomes. During winter time the stem bases contained 2 to 2.5 % of sucrose. Plant height and aboveground biomass were also higher in molinion site.     

Physiological Factors Limiting Grain Size in Wheat

The effects on grain size of changing the supply of assimilates,by thinning before anthesis or by shading the plants or by halvingthe ears either early or late in grain growth, were studiedin two glasshouse experiments with Kleiber spring wheat (Triticumaestivum L.), in 1976 and 1977. Late treatments had no effect,presumably because little grain growth occurred thereafter.Thinning the plants before anthesis increased, and shading theplants soon after anthesis decreased grain size. Halving theears soon after anthesis increased the size of the remaininggrains, but grain weight per ear decreased. The effect on grainsize of halving the ear tended to be smaller under conditionsmore favourable for photosynthesis, except when the plants werethinned before anthesis. Shading decreased the total amountof nitrogen per culm and the proportion of total nitrogen recoveredin the ear. Halving increased the retention of nitrogen in thestem of unshaded shoots and had no effect on nitrogen distributionwithin shaded shoots. In 1977 halving the ear increased the rate of dry matter accumulationin the grain throughout the grain filling period, but in 1976the increase in dry weight was faster in the grains of halvedears only during early grain growth. Later the grains in halvedand intact ears increased in dry weight at the same rate, eventhough the supply of photosynthate and the capacity of the grains(as measured by volume) were greater in the halved ears. Theseresults are discussed in relation to the influence on finalgrain weight of assimilate supply and the storage capacity ofthe grain.     

THE EFFECT OF GIBBERELLIC ACID ON THE ABSORPTION AND TRANSLOCATION OF PHOSPHORUS-32 BY BEAN PLANTS

Linck , A. J., and Theodore W. Sudia . (U. Minnesota, St. Paul.) The effect of gibberellic acid on the absorption and translocation of phosphorus-32 by bean plants. Amer. Jour. Bot. 47(2) : 101—105. Illus. 1960.–Plants of Phaseolus vulgaris, variety ‘Black Valentine,‘ treated with 1 p.p.m. gibberellic acid supplied to the roots for 4 hr. were compared with nontreated. plants for phosphorus-32 uptake. Plants treated with gibberellic acid where transpiration was either rapid or restricted absorbed more phosphorus-32 than those not treated. More phosphorus-32 was recovered from plants free to transpire than from plants in high humidity. In plants free to transpire, significantly more phosphorus was present in the treated plants after 28 hr. and significantly more phosphorus-32 accumulated in treated plants in those parts actively growing, i.e., stem apex, second internode and first trifoliate leaf, and in the roots. For plants in high humidity atmosphere significantly more phosphorus-32 was absorbed by the treated plants at the end of 4 hr. than in the non-treated plants and this difference was maintained throughout all times of harvest. For plants in high humidity atmosphere, significantly more phosphorus-32 accumulated in the lower portions, i.e., roots, hypocotyl, first internode and primary leaves, of treated plants than of non-treated plants, while the differences for the second internode, the first trifoliate leaf and the stem apex were not significant between treated and non-treated plants.